This invention lies in the field of rapidly crystallizing polyethylene terephthalate molding resin blends.
Various crystallizing and nucleating agents (including esters) are known for promoting the crystallization rate of polyethylene terephthalate from a melt phase. Such a rate increase in crystallization is desirable for purposes of shortening molding cycle times and lowering molding temperatures.
Bier et al in U.S. Pat. No. 4,223,113 teach combinations of polyalkylene terephthalate and "an oligomeric polyester having a minimum polymerization degree of 2 and a maximum number-average molecular weight of about 6,000, said oligomer being free of any substitutes which are substantially reactive with said high molecular weight polyalkylene terephthalate under injection molding conditions" (see, for example, claim 1 of Bier et al '113). The oligomers can be formed of sebacic or adipic acid with diols and monohydric alcohols.
Hecht et al in U.S. Pat. No. 4,338,243 and Deyrup in Re No. 32,334 teach the use of esters of aromatic carboxylic acid and alcohols as polyethylene terephthalate crystallization promoters.
However, so far as now known, no one has previously taught or suggested the use of medium number-average molecular weight aliphatic polyesters as reactive crystallization promoters for polyethylene terephthalate.